Reading Your Fish Finder -101

A Fish Finder is a must if you’re going to step up your fishing game.


This week I thought I would write about something that eludes most fisherman, understanding their Fish Finder. It’s true you can catch fish casting to the bank year round, but you will catch more fish and bigger fish if you learn to find them off shore. With multiple electronic units reading sonar, Side Scan, and Down Scan, it is very easy to get overwhelmed. Still, it seems that everyone from your professional bass angler to the weekend recreational fisherman now has $1000 – $3000 in electronics on their kayak. There are a lot of people that own these electronics that couldn’t tell hard bottom from a stump, or a fish from clutter on the screen. So we wanted to hopefully clear up some things on reading your electronic fish finders.


There are three basic types of fish finders:

  • Dedicated fishfinders with traditional transducers – AKA Sonar
  • Side imaging and down imaging
  • Fishfinder/Chartplotter Combos
Fish Finder

SonarHub by Lowrance

I will speak mainly to the traditional fish finder that most folks have – sonar. Let’s start by defining sonar, which is an acronym for SOund, NAvigation and Ranging. It is not visual. It’s all about sound and works as well in the dark as it does in the light. What you see on your electronics screen is nothing more than the units visual interpretation of sound.



Sonar detects three objects in the water by sending and receiving sound waves.

  • Suspended Objects
  • Objects on the bottom
  • The actual lake bottom itself

It does this through a crystal in the transducer which allows it to measure time over distance. That is, how long does it take for a sound wave to leave the transducer, bounce off of something and then return to the transducer as our boat is moving across the water’s surface? That gives us distance.

What am I seeing?

Chirp Digital Sonar by Hummingbird

The only thing that’s (real time) on your sonar screen is on the far right side. Unless you’re running an old paper graph, the screen isn’t moving at all. What’s happening is that lights — your screen is a grid of tiny lights — are being sequentially turned off behind the signal which creates the illusion of movement. Everything past the right side of the screen is way behind you, so far behind you that you could almost never cast to it.

Approximately 50 percent of the sound waves are concentrated in the power zone (cone) under the transducer. That circle is roughly one-third of the depth of the water you’re in. So, if you’re over 12 feet of water, your most detailed screen information comes from an area about 4 feet across directly below your transducer.

If you mark an object in the water and want to know what it’s actual size is, look at the top (center) of the arch. If it’s big, the center will be wide, and if it’s small the center will be narrow.

Most anglers think an arch is a fish, which is possible. It’s also possible that it’s a waterlogged stick or a submerged beer can

What next?

For more information on how to read your fish finder, check out Jeff “Kolo” Kolodzinski’s video on Youtube titled “How to Read Fish Finder Sonar Technologies.

I hope this helps you understand fish finders more than you did before reading this. If you have one of these units on your kayak, I challenge you to get out there and really put some effort into understanding your electronics. In the end, you will benefit from getting the most of if it.

One Simple Question: What aspect of reading fish finders would you like Russ to cover next?

Want to see more tips on how to catch more fish? Click here

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